Over the last five years, the Mexican drug war has claimed the lives of an estimated 40,000 civilians and drug traffickers. British journalist Ioan Grillo describes it as "a bloodbath that has shocked the world."

In his new book, El Narco, Grillo takes a close look at the Mexican drug trade, starting with the term el narco, which has come to represent the vast, often faceless criminal network of drug smugglers who cast a murderous shadow over the entire country.

"People struggle to really understand what this force is," Grillo tells NPR's Ari Shapiro. "You talk about el narco being behind 30 bodies on the street and el narco threatening politicians, but who really are these people and what really are they?"

He says when he first arrived in Mexico in 2001, traffickers used gangbangers to carry out their assassinations — but not anymore.

"Now they have fully fledged militias with AK-47s, [rocket-propelled grenades]," Grillo says, "and they have become something very fearsome and very dangerous within Mexico."

'El Narco' As Boss

Over the years, el narco has also become deeply embedded in Mexican society. In some communities, the local cartel serves as the biggest business and the biggest employer. According to Grillo, the violent Zetas cartel has even been known to post want ads.

"The Zetas put up adverts on the street on blankets with a phone number saying 'Why are you going to work on a bus? Join us. We'll get you a good salary. If you're an ex-military guy, we'll give you a job,'" Grillo says.

And just as the wealthy might finance culture, so do the cartels. Though, according to Grillo, traffickers' contributions are often more about getting their own name out there.

"One way to do that is to pay somebody to write something about them," he says. "Now if you go to places where there is a big history of drug trafficking, like Sinaloa state, and you talk to these musicians you will find that any one of them will have a price they charge to write a song, to compose a ballad about somebody."

A cartel's patronage can go a long way. Grillo says some Sinaloan communities call drug traffickers los valientes, Spanish for the brave.

Still, not every story of cartel patronage ends well. In his book, Grillo recounts hearing the story of the musician one low-level trafficker had commissioned to write a particularly catchy song about him. Grillo writes,

Soon everyone played it on his car stereo. "The crime bosses were like, 'Bring me the guy from that song. I want him to do the job for me.' So he rose through the ranks because of the song." "So what happened to him now?" I asked. "Oh, they killed him. He got too big. It was because of the song really."

The Business Side Of Trafficking

At the root of the current violence in Mexico is a lucrative drug trade that offers traffickers $50 for every dollar they invest.

"You can buy a kilo brick of cocaine in Columbia for $2,000. When you sell it at a gram level in the U.S., you can turn that into some $100,000," Grillo says. "That area of buying the cocaine from Columbia and selling it to Americans is the area dominated by Mexican cartels."

And those cartels have grown the trade to incredible proportions. In his book, Grillo describes a visit a Mexican military base that was used to store drugs that had been confiscated from the cartels.

As we step inside, a cocktail of mystic toxic smells greets us. To the left, towers of cling-wrapped marijuana loom above our heads. To the right are huge sacks of cut-up ganja plants and enough seeds to give birth to a forest of psychedelic weed. Walking forward, we stumble into a pile of giant, blue metal saucepans ... The white sludge of raw methamphetamine fills the pan like a foul stew of ice and sour milk. In a corner, we catch sight of a much older Sinaloan product, black-tar heroin, which looks like jet-black Play-Doh, oozing out of yellow cans.

While no one knows the exact numbers, Grillo says the trade in such products is estimated to be worth tens of billions of dollars.

'An Escape' In Ciudad Juarez

There's no question that Mexican society has been traumatized by the violence of the last five years; but, through it all, some have found a way to cope.